An automatic shift device automatically shifting the gear stages of an automated transmission by a control unit, which is an ECU, actuating a driving motor is known. For example, in a technology disclosed in JP3709955B, hereinafter referred to as Reference 1, an ECU actuates a driving motor of an automatic shift device and moves a sleeve, which is connected to the driving motor and in rotary engagement with an input shaft, in an axial direction of the input shaft with a predetermined torque, when shifting a gear stage. The protruding portion of a dowel provided on the sleeve engages with the recessed portion of the dowel provided on a gear that is idly rotatably supported by the input shaft so as to integrally rotate the sleeve and the gear. Accordingly, rotational driving power is transmitted to an output shaft that is in rotary engagement with the gear. In the above case, a synchronizer mechanism is not used on bringing the sleeve and the gear into rotary engagement. As a result, the sleeve and the gear are not smoothly engaged every time. In other words, there may be a case where the protruding portion of the dowel provided on the sleeve is not engaged with the recessed portion of the dowel provided on the gear. An end portion of the protruding portion of the dowel may contact the flat surface of a protrusion at a position between the protruding portion of the dowel and the recessed portion of the dowel so that the protruding portion of the dowel and the recessed portion of the dowel synchronously rotate or slide on each other while rotating relative to each other. In the technology disclosed in Reference 1, as a countermeasure for such case, the rotation angle of the driving motor, which in other words is the operation stroke of the sleeve, is detected first, after the driving motor is actuated. In a case where the detected operation stroke is a stroke that is unlikely to reach a predetermined stroke that corresponds to the stroke at a time at which the sleeve is completely engaged with the gear, the sleeve and the gear are determined as not in an engaged state so that a re-entry control, or a retry control, is performed. The re-entry control is a control that temporarily reduces a torque applied from the driving motor for moving the sleeve so that the sleeve and the gear rotate relative to each other, and then retries entry of the sleeve into the recessed portion of the dowel by re-applying the predetermined torque on the sleeve. At the moment the protruding portion of the dowel and the recessed portion of the dowel come to the same phase, the predetermined torque is re-applied on the sleeve to move the sleeve so as to make the protruding portion of the dowel enter the recessed portion of the dowel. As a result, the sleeve and the gear are engaged with each other and are made to integrally rotate.
In the automatic shift device disclosed in Reference 1, a determination that the sleeve and the gear are not in an engaged state, which in other words is a determination that that the stroke of the sleeve is unlikely to reach a predetermined stroke that corresponds to the stroke at a time at which the sleeve is completely engaged with the gear, is determined with a timer and determined by whether or not a predetermined estimated time has elapsed. The predetermined estimated time is required to be defined at a length of time equal to or longer than the length of time required by the sleeve to smoothly reach the predetermined stroke. As a result, a lengthy time is required to determine that the sleeve and the gear are not engaged and a total shift time becomes long.
A need thus exists for an automatic shift device for an automated transmission for a vehicle, which is not susceptible to the drawbacks mentioned above.